RX Family
Hardware Design Guide
R01AN1411EJ0110 Rev.1.10
Page 21 of 32
Oct.26.21
2.5 Analog Input Pins
Connect each analog input pin to GND via a capacitor. Wiring between the analog input pin and capacitor
and wiring between the AVSS pin and capacitor must be the same length and as short as possible. Do not
run the trace for the analog input pin parallel to or across other traces (traces with large current flows or rapid
level changes), and shield the trace for the analog input pin with the GND trace. The GND traces used for
shielding should be at least 0.3 mm wide and there should be a space of 0.3 mm to 2.0 mm between them
and adjacent traces.
Board design hint
If noise impinges on the analog input pins, the waveforms may become distorted, possibly reducing
A/D converter accuracy. An external capacitor can be used to reduce noise.
An external capacitor can also be used to achieve high-speed conversion. This requires that sufficient
electrical charge has accumulated in the external capacitor before conversion starts to reduce the
signal source impedance of the input capacitor of the sample and hold circuit. Note that if the voltage
level of the analog input pin changes (in continuous scan mode, for example), causing the external
capacitor charge to be renewed, an adequate electrical charge cannot be accumulated. In this case,
do not connect an external capacitor.
Figure 2.17 shows an example analog input pin circuit configuration, and Figure 2.18 shows an example
analog input pin wiring pattern.
ANxxx
*
1
AVSS
RX Family MCU
Sensor
GND
OUT
S/H
circuit
Note: 1. ANxxx represents an analog input pin.
Figure 2.17 Example Analog Input Pin Circuit Configuration
